1. Technical Field
The present invention relates to a position calculating method and a position calculating device.
2. Related Art
A GPS (global positioning system) is widely known as a positioning system using positioning signals. The GPS is included in a position calculating device contained in a cellular phone, a car navigation device, or other units. The GPS performs position calculation for obtaining three-dimensional coordinates indicating the position of the GPS and time errors based on information about positions of plural GPS satellites and pseudo distances between the plural GPS satellites and the GPS.
For calculating positions, position calculation by least squared method and position calculation using Kalman filter are known. As a technology associated with the Kalman filter, a method which estimates the condition of the position calculating device by using the moving speed and azimuth of the position calculating device detected by a speed sensor and an azimuth sensor as inputs to the Kalman filter has been disclosed in U.S. Pat. No. 4,680,715.
According to the position calculation using Kalman filter in related art, calculation is generally performed using fixed parameters. However, when the position calculating device is included in an electronic device such as a cellular phone and a car navigation system, the position calculating device constantly changes movement condition in various ways such as stop, rotation, acceleration, and deceleration since the user carrying the cellular phone or the automobile containing the car navigation system are movable.
Thus, when position calculation is performed using fixed parameters, such phenomena as “position lag” in which the times of the calculated positions obtained by position calculation lag the times of the actual positions, “position lead” in which the times of the calculated positions obtained by position calculation lead the times of the actual positions, and “position jump” in which calculated positions largely deviate from the actual positions are produced. In this case, accuracy in position calculation lowers.